1. Field of the Invention
The present invention relates to the storage and retrieval of data on magnetic tape, and more particularly, to a mechanism for opening the tape access door of a tape cartridge to expose a segment of magnetic tape inside the cartridge for engagement by a transducer head.
2. Description of the Related Art
Magnetic tape has long been used as a storage media for audio, video and computer information. Tape cartridges have been used extensively because they provide a convenient way to house and support a length of magnetic tape for engagement by a transducer in a tape drive while protecting the tape upon removal of the cartridge. Tape cartridges with dual reels are widely used because they eliminate the need to thread a leader outside the cartridge or utilize an endless loop single reel arrangement. Examples of dual reel tape cartridges that have been extensively commercialized are the Phillips cassette used for audio recording, the VHS cassette used for video recording, and the DC600 data cartridge used for back-up storage of computer data files stored on hard disk drives. The latter data cartridge is disclosed in U.S. Pat. No. 3,692,255 of Von Behren assigned to Minnesota Mining and Manufacturing Corporation.
Many prior art magnetic tape cartridges have included a moveable door for opening and closing a tape access opening. Conventionally, the door is opened when the tape cartridge is inserted into a tape drive in order to expose a segment of magnetic tape which is engaged by a transducer head. Typically a tape access door either pivots or slides open and closed. When the tape cartridge is removed from the tape drive, the tape access door is usually closed by a bias spring. This protects the magnetic tape within the tape cartridge from contact with a user's hand. The closed tape access door also prevents dust and other debris from entering the tape cartridge. Such dust and debris can contaminate the tape and result in subsequent errors in reading and/or writing data onto the tape.
The design of a door opening mechanism for a tape drive is critical to its reliable operation. Clearly if the tape access door mechanism fails to properly open the door, data cannot be read from the tape or recorded onto the same. A worse consequence is that the tape cartridge, with its tape access door fully closed, may be jammed or forced into contact with the delicate face of the transducer head. The transducer head is typically one of the most expensive items in a tape drive. It often has a delicate structure including laminate assemblies or thin film elements which may be either inductive or magnetoresistive. These elements can be easily damaged.
In most cases, when a tape cartridge is inserted into a tape drive the initial part of the insertion process is done manually. The cartridge is often inserted into a carriage which is thereafter automatically driven by a motor to translate the cartridge to a head. In such a drive, it is critical that the tape access door opening mechanism not only operate reliably, but that it open the tape access door in the proper time sequence so that the door will clear various other structures within the tape drive yet end up sufficiently open to permit proper head engagement. To further complicate matters, it is frequently necessary for tape drives, particularly those that serve as peripheral storage devices for computers, to fit within very constrained industry standard mechanical form factors. In such cases, the space available for the door opening mechanism is extremely limited. This often limits the range of motion of the tape access door.
Another very important consideration in designing a tape access door opener for a tape cartridge is that the cartridge must be registered in a very precise manner in order to enable high density, multi-track reading and writing. This usually requires that a data cartridge have a rigid metal base or mount plate which can be clamped against fixed datums. It is usually necessary to move the mount plate perpendicular to its plane during the registration process along a Z axis. Thus, the tape access door must be capable of accommodating such transverse movement of data cartridge away from its cartridge insertion axis. Also, it may be necessary to move the data cartridge in both the X and Y axes of the mount plate during the loading process. Therefore, a door opener should be capable of accommodating movement in the X, Y and Z planes.
Finally, a tape access door mechanism must be compliant to variations in the cartridge loader mechanism and cartridge. This is necessary to ensure that the door ends up fully open.
Thus, there is a strong need to provide a reliable and compact tape access door opening mechanism for a given tape cartridge design. Preferably such a tape access door opening mechanism should not include motors, solenoids or other electro-mechanical activating mechanisms. Such mechanisms not only consume additional space, but they add to the cost of the tape drive and represent potential failure points. As already explained, the failure of the tape access door opening mechanism can be catastrophic, both because it prevents the tape drive from operating, and because such a failure can result in the destruction of the transducer head.
VHS, BETA and 8 mm video tape cartridges all incorporate a tape access door which rotates about an axis parallel to the plane of the base surface thereof through which the reel hubs are accessed. Many tape drives which utilize these video tape cartridges include motor driven auto loading mechanisms. Typically the video cartridge is manually inserted into a carriage which then reciprocates downwardly to register the hubs over drive spindles. Upon insertion of the video tape cartridge, there is normally a tab on the video cartridge which is depressed by a projection on the carriage to unlock the tape access door. The tape access door is then lifted open by a simple finger or flange on the drive frame adjacent the carriage as the tape cartridge is translated to engage the drive spindles.
The tape access door of the data cartridge disclosed in the aforementioned U.S. Pat. No. 3,692,255 pivots open about an axis substantially perpendicular to the rigid Aluminum mount plate of the cartridge (Z axis movement). The tape access door of this cartridge is positioned along one of the major side edges of the tape cartridge. Many door opening mechanisms have been utilized in conjunction with this data cartridge which has been widely commercialized under the model numbers DC300 and DC600. One of the earliest examples of a door opening mechanism for the DC300/DC600 data cartridge is disclosed in U.S. Pat. No. 4,573,091 of Barton, Jr., et al. The data cartridge is inserted on a tray. A spring biased door opening linkage connected between the tray and the frame of the tape drive pushes on the end of the tape access door. This partially opens the door in the proper time sequence to clear the transducer head without exceeding the five and one-quarter inch form factor.
A later example of a door opening mechanism for opening the tape access door of the DC300/DC600 data cartridge is shown in U.S. Pat. No. 5,025,334 of Perona, et al. In the tape drive disclosed in that patent, the tape is manually loaded onto a tray which is then automatically moved forwardly and then transversely. The end of the tape access door is engaged by a door opener comprising an L-shaped member with orthogonal arms. The member is pivotally mounted to a vertical pin secured to the front right corner of the tray. A torsion spring surrounds the pin and biases the member in a clockwise direction.
An improved magnetic tape cartridge particularly well suited for high capacity computer data storage is disclosed in U.S. Pat. No. 5,294,072 of Don G. East, et al. assigned to International Business Machines Corporation. FIG. 1 is a perspective view of the prior art magnetic tape cartridge A with improved tension control which is described in detail in the aforementioned U.S. Pat. No. 5,294,072, the entire disclosure of which is specifically incorporated herein by reference.
The tape cartridge A (FIG. 1) includes a generally rectangular housing formed by a rigid Aluminum mount plate B and a box-like molded plastic cover C. The cover C includes a pair of holes exposing two toothed tape reel hubs (not visible). A length of magnetic tape (not shown) is wound between the tape reels (not shown) inside the plastic cover C.
A forward end of the tape cartridge A (FIG. 1) is provided with a tape access door D which pivots about an axis substantially perpendicular to the plane of the mount plate B. The tape access door D is shown pivoted to its fully open position in FIG. 1, thereby exposing a segment of the magnetic tape (not shown) through a head access opening formed in the forward end of the plastic cover C. The door D is biased to its closed position by a torsion spring (not shown) associated with the pivot pin of the door D. A slot E is formed on one side wall of the door D for engagement by a pin of a door opener. The slot E is straight except for a rearward end thereof which angles open on an the outer wall of the door D. The slot E also opens on the side of the door D along the entire length of the slot.
The magnetic tape rides around and between a pair of tape guides F and G (FIG. 1) secured to the mount plate B. The inside of the tape access door D (FIG. 1) is provided with a pseudo-head H. When the tape access door D is in its closed position, the pseudo-head H occupies the space otherwise occupied by the tape transducer or head of a tape drive when the head is mated with the exposed segment of magnetic tape. When the pseudo-head H engages the tape it prevents the tape from being drawn taught between the guides F and G. When the drive clutches of the tape drive are disengaged from the reel hubs, the rotational position of the tape reels is locked. These two improvements maintain proper tape tension when the cartridge is removed from the tape drive.